The present invention relates to semiconductor wafer processing techniques, and particularly to a technique effective for use in handling semiconductor wafers when the semiconductor wafers are processed to a very small thickness of 100 xcexcm or below.
In semiconductor devices that we required to be thin as well as of high density and small size, such as semiconductor devices applied to IC cards, ever thinner packages, are used, such as TQFP (thin quad flat package) and TSOP (thin small outline package). In order to manufacture such packages, it is necessary to make the semiconductor wafers particularly thin. Here, the known techniques for making the semiconductor wafers thin, as for example described in xe2x80x9cPRACTICAL LECTURES VLSI PACKAGING TECHNOLOGY (the second volume)xe2x80x9d published by NIKKEI BP Co.,Ltd. on May 31, 1993, pp. 12 to 14, are grinding, chemical etching and lapping. As in the publication, grinding is a technique for grinding rear surface of a semiconductor wafer with a diamond grindstone, a etching is the technique for etching the rear surface of a semiconductor wafer with a mixture of chiefly fluoric acid and nitric acid while the semiconductor wafer is being rotated with high speed, and lapping is a technique for grinding the rear surface of a semiconductor wafer with abrasive grains.
The thinning process by the grinding or lapping is able to grind semiconductor wafers of general thickness, or about 625 xcexcm (or 725 xcexcm) to a thickness of about 300 xcexcm, but has a difficulty when trying to grind to a thickness of, for example, 100 xcexcm or below because the semiconductor wafer might be cracked even under strict care when removing it from the grinder. Even if the wafer is not cracked, it is remarkably warped depending on the stress in the passivation film on the wafer surface and the internal stress of the wafer. This warp causes operational problems in the following processes such as dicing. In addition, it is difficult to process large-diameter semiconductor wafers, or 12-inch or above wafers to a specified level of flatness and uniformity.
Moreover, in the thinning process by etching, since the wafer is rotated at high speed, an excessive stress is exerted on the semiconductor wafer by the pins that hold its outer peripheral portion at a plurality of locations, thus breaking the wafer. Furthermore, a warp will occur due to the internal stress as in the grinding.
In order to solve the above problems, the inventors have found to fix the semiconductor wafer to a certain support base with tape and process it after various examinations. However, normal tape is also discarded after use in the process of each wafer, thus increasing the cost, or causing a new problem.
Accordingly, it is an object of the invention to provide a technique capable of making semiconductor wafers thin without any crack by solving the above technical problems.
It is another object of the invention to provide a technique capable of making semiconductor wafers thin under easy operation.
It is still another object of the invention to provide a technique capable of making semiconductor wafers thin without any warp.
It is a further object of the invention to provide a technique capable of making semiconductor wafers thin at low cost.
The features of the invention, and the above objects of the invention together with other objects will be best understood by the following description, taken in conjunction with the accompanying drawings.
A typical one of the inventions disclosed in this application will be described briefly as below.
The semiconductor wafer processing method according to the invention includes a first step of preparing a plate-like or film-shaped carrier that is formed of a base and an adhesive member provided on one surface of the base, a second step of producing a wafer composite by bonding a semiconductor wafer to the carrier in such a manner that the rear surface of the wafer with no circuit elements formed therein is opposite to the carrier, and a third step of making the semiconductor wafer thin by spin-coating an etchant on the rear surface of the semiconductor wafer of the wafer composite that is supported with its semiconductor wafer side up.
In this semiconductor wafer processing method, the semiconductor wafer of the wafer composite is made to have a larger diameter than the carrier so that all the outer peripheral edge of the semiconductor wafer overhangs from the carrier when the wafer composite is formed by bonding the wafer on the carrier. In the third step, the semiconductor wafer can be thinned while a gas is being blown from below against the wafer composite. In addition, the semiconductor wafer may be made to have a diameter equal to or smaller than the carrier so that the peripheral edge of the wafer does not overhang from the carrier when the wafer composite is formed.
Moreover, after the semiconductor wafer is thinned by the third step, a fourth step and a fifth step may be provided. The fourth step is for sticking the rear side of the wafer on a dicing sheet and peeling off the carrier, and the fifth step is for dicing the semiconductor wafer on the dicing sheet into individual semiconductor chips.
The semiconductor wafer processing method of the invention includes a first step of preparing a semiconductor wafer with a passivation film formed on its main surface in which circuit elements are already built, a second step of preparing a plate-like or film-like carrier that is formed of a base and an adhesive member provided on one surface of the base, a third step of producing a wafer composite by bonding the semiconductor wafer to the carrier in such a manner that the rear surface of the wafer with no circuit elements formed therein is opposite to the carrier, and a fourth step of holding the wafer composite with its semiconductor wafer side up and spin-coating an etchant on the rear surface of the semiconductor wafer thereby to thin the semiconductor wafer. In this case, after thinning the semiconductor wafer at the fourth step, it is possible to add a fifth step of attaching the rear surface of the semiconductor onto a dicing sheet and peeling off the carrier from the wafer composite, and a sixth step of dicing the semiconductor wafer left on the dicing sheet into individual semiconductor chips.
The IC card producing method according to the invention includes a first step of preparing a plate-like or film-like carrier that is formed of a base and an adhesive member provided on one side of the base, a second step of producing a wafer composite by bonding a semiconductor wafer to the carrier in such a manner that the rear surface of the wafer with no circuit elements formed therein is opposite to the carrier, a third step of holding the wafer composite with its semiconductor wafer side up and spin-coating an etchant on the rear surface of the semiconductor wafer thereby to thin the semiconductor wafer, a fourth step of attaching the thinned rear surface of the semiconductor wafer to a dicing sheet and peeling off the carrier from the wafer composite, a fifth step of dicing the semiconductor wafer left on the dicing sheet into individual semiconductor chips, a sixth step of reducing or loosing or losing the adhesion of the dicing sheet, a seventh step of mounting one or ones of the semiconductor chips on a card substrate at chip-mounting positions, and an eighth step of producing an IC card by using the card substrate with the semiconductor chip or chips mounted.
According to the invention, there is provided an IC card producing method including a first step of preparing a semiconductor wafer with a passivation film formed on its main surface in which circuit elements are already built, a second step of preparing a plate-like or film-like carrier that is formed of a base and an adhesive member provided on one surface of the base, a third step of producing a wafer composite by bonding a semiconductor wafer to the carrier in such a manner that the rear surface of the wafer with no circuit elements formed therein is opposite to the carrier, a fourth step of holding the wafer composite with its semiconductor wafer side up and spin-coating an etchant on the rear surface of the semiconductor wafer thereby to thin the semiconductor wafer, a fifth step of attaching the thinned rear side of the semiconductor wafer to a dicing sheet and peeling off the carrier from the wafer composite, a sixth step of dicing the semiconductor wafer left on the dicing sheet into individual semiconductor chips, a seventh step of reducing or loosing or losing the adhesion of the dicing sheet, an eighth step of mounting one or ones of the semiconductor chips on a card substrate at chip-mounting positions, and a ninth step of producing an IC card by using the card substrate with the semiconductor chip or chips mounted.
When bumps are formed at the chip electrodes of the semiconductor wafer in the IC card producing methods of the invention, the thickness of the adhesive member provided on the base should be equal to or larger than the height of the bumps. In addition, at the seventh step, it is desirable to directly mount the semiconductor chips on the card substrate from the dicing sheet.
Moreover, the carrier in the invention is used in the semiconductor wafer processing method, and its adhesive member comprises an elastically flexible suction pad for sucking the semiconductor wafer by vacuum. In this carrier, the suction,pad may have a size large enough to suck substantially an entire surface of the semiconductor wafer. In addition, it may be formed in a ring shape along the outer periphery of the semiconductor wafer. Also, a plurality of such suction pads may be provided over an entire surface of the base in order to hold the semiconductor wafer at a plurality of locations.
In addition, the carrier in the invention is used in the semiconductor wafer processing method, and its adhesive member comprises a suction groove that is formed in the base to be communicated with a vacuum hole connected to a vacuum pump so that the semiconductor wafer is sucked by vacuum and peeled off from the carrier by restoring to atmospheric pressure.
Also, the carrier in the invention is used in the semiconductor wafer processing method according to the invention, and its adhesive member is constituted by a plurality of suction holes which are formed in one surface of the base at different locations to be communicated with a vacuum hole connected to a vacuum pump so that the semiconductor wafer is sucked by negative pressure and peeled off from the carrier by restoring to atmospheric pressure.
Moreover, the carrier in the invention is used in the semiconductor wafer processing method according to the invention, and its adhesive member comprises a porous member that has a great number of small holes and is provided on one surface of the base for the small holes to be communicated with a vacuum hole connected to a vacuum pump so that the semiconductor wafer is sucked by vacuum and that it is peeled off from the carrier by restoring to atmospheric pressure.
Also, the carrier in the invention is used in the semiconductor wafer processing method according to the invention, and its adhesive member includes an exfoliation portion coplanar with the base to form a plurality of small recesses, and gelled silicone interposed between the peeling portion and the semiconductor wafer to make the base adhere to the semiconductor wafer, whereby when the surroundings of the exfoliation portion are evacuated the silicone is sunk in the recesses so as to be peeled off from the semiconductor wafer. The exfoliation portion of the carrier may be a net or an irregular surface formed on the base.
In addition, the carrier employed in the semiconductor wafer processing method according to the invention has its base made of a transparent material and its adhesive member made of a UV cure-type adhesive of which the adhesion is reduced or lost by ultraviolet rays radiated through the base so that the carrier can be peeled off from the semiconductor wafer.
Also, the adhesive member employed in the semiconductor wafer processing method according to the invention is made of a temperature activation type adhesive of which the adhesion is reduced or lost by temperature change so that the carrier can be peeled off from the semiconductor wafer. The temperature activation type adhesive of this carrier may have such a characteristic that its adhesion is reduced or lost at a low temperature.
The adhesive member employed in the semiconductor wafer processing method according to the invention is a liquid that acts as an adhesive in such a manner that the semiconductor wafer and the base are made in intimate contact with each other by the interfacial force exerted therebetween and that the semiconductor wafer is peeled off from the base by ultrasonic waves.
The base of the carrier should be made of an acid-resistant material, for example, compacted fibrous fluororesin.
Thus, since the semiconductor wafer thinning process is performed on the wafer composite formed by bonding the semiconductor wafer to the carrier, any cracks can be prevented from occurring even with no strict care when the semiconductor wafer is thinned. In addition, since the reduction of the rigidity of the thinned semiconductor wafer can be compensated for by the carrier so that release of the stress in the passivation film is prevented, the semiconductor wafer is not warped. Thus, the semiconductor wafer can be stably processed to be extremely thin.
Moreover, since the wafer composite can be handled in the same way as the semiconductor wafer having a normal thickness before thinning, any cracks can be prevented form occurring on the semiconductor wafer even with no strict care, and the work for thinning can be made with ease.
In addition, since the carrier of the wafer composite is supported so that no unnecessary stress is exerted on the semiconductor wafer, no warp occurs, and thus the semiconductor can be thinned with high quality.
If the semiconductor wafer is fixed to the base by the suction pad, the carrier need not be discarded after use and can be simplified in its construction, and thus the semiconductor wafer can be thinned at low cost.
If the wafer composite is formed by attaching the semiconductor wafer to the base to overhang from the carrier, and spin-coated with an etchant while gas is continuously blown against this wafer composite, the etchant can be surely prevented from flowing around the outer peripheral side into the main surface, whereby the circuit elements are not damaged.
If the wafer composite is so formed that the outer periphery of the semiconductor wafer does not overhang from the carrier, the etchant is prevented from flowing around the peripheral side into the main surface, and thus it is not necessary to blow gas against the wafer composite. Moreover, since the thinned semiconductor wafer does not overhang from the carrier, the wafer composite can be easy to handle. Also, since the entire main surface of the semiconductor wafer is covered by the carrier so that it is shielded from the external atmosphere, the rear surface of the semiconductor wafer can be etched even by dipping.
If an IC card is produced by using semiconductor chips that are produced by dicing the thinned semiconductor wafer, the IC card can be made thinner than the conventional IC card.
If the thickness of the adhesive member provided on the base is made equal to or larger than the height of the bumps formed on the semiconductor wafer, the entire carrier is made in intimate contact with the semiconductor wafer so that both are not peeled off from each other. Also, if the semiconductor chips are directly mounted on the card substrate from the dicing sheet, the additional moving operation for the semiconductor chips can be omitted, and thus throughput can be improved.
The peeling operation after thinning can be simplified by taking the vacuum suction structure of the carrier for sucking the semiconductor wafer, or by using an adhesive member formed of a peeling portion and an adhesive sheet or formed of UV cure-type adhesive or temperature activation adhesive. Moreover, since the semiconductor wafer is always kept flat along the base, the warp of the semiconductor wafer can be effectively suppressed.
Since the carrier formed of an reversible temperature activation type adhesive can be repeatedly used in the thinning process, the thinned semiconductor wafer can be mass-produced at low cost.
Since the carrier having the base made of an acid resistant material can be repeatedly used in the thinning process, the thinned semiconductor wafer can be mass-produced at low cost.
Since the base may be made of compacted fibrous fluororesin having a feature of resistance against acid, it is possible to use various different adhesives such as temperature activation type adhesives with weak adhesion to the base.